ER fluid is known which produces an electrorheological (hereinafter, “ER”) effect that the degree of apparent viscosity increases by applying a voltage thereto. The degree of viscosity of the ER fluid can be reversibly and freely changed by varying a voltage applied to the ER fluid, and furthermore, its responsiveness to change in voltage is excellent.
The ER fluid generally has a state where dispersal phase particles (ER particles) are dispersed in an electrical-insulation dispersion medium such as silicone oil or the like. Therefore, if the ER fluid stands for a long time, the ER particles precipitates and aggregates, and a stable ER effect is less easily obtained.
Consequently, in order to prevent such ER particles from precipitating and aggregating, ER gel is proposed which holds an electrical-insulation dispersion medium having ER particles which are dispersed in a gel skeleton (for example, refer to Patent Document 1).
Such ER gel has a low-frictional state in which a contact area is reduced as the ER particles float the surface thereof when a voltage is not applied thereto, in contrast, a frictional force at the surface thereof increases as the ER particles precipitate in the gel when a voltage is applied. Accordingly, with an ER device in which a sheet-shaped ER gel are disposed between two electrodes, it is possible to electrically control the frictional force. For this reason, such ER device is expected to use for devices utilizing a frictional force such as a vibrational absorption device (a damper or the like), an impact absorption device (a bumper or the like), a locking device (a clamp or the like), or the like.